Field of the Invention
This disclosure is related to a sheet stacking apparatus on which a sheet is stacked, and an image forming apparatus.
Description of the Related Art
Hitherto, a configuration in which a position of a sheet on a stacking tray in a sheet discharging direction is aligned by discharging the sheet on which an image is formed toward the stacking tray and abutting the discharge sheet to an abutment member arranged on the upstream side of the sheet in the sheet discharging direction has been known. In such a configuration, a leading end of a sheet discharged toward the stacking tray (hereinafter, described as “discharge sheet”) comes into contact with a sheet already stacked on the stacking tray (hereinafter, described as “stacked sheet”).
When a leading end of a discharge sheet comes into contact with a stacked sheet, the stacked sheet is easily pushed out to the downstream side of the sheet in the sheet discharging direction. As such a configuration in which pushing-out of a stacked sheet to the downstream side in the sheet discharging direction due to a discharge sheet is prevented, a method of blowing air to a sheet or a stacking tray from the bottom of the discharge sheet is described in JP-A-2014-47047.
In a configuration in which air blowing is performed in order to prevent pushing-out of a stacked sheet due to a discharge sheet, in a case in which a volume of air blown toward a discharge sheet is large, a landing spot of the discharge sheet is easily located on the downstream side of the stacking tray in the sheet discharging direction. In this case, a movement distance of the discharge sheet from stacking to bumping into an abutment member becomes long, a behavior of the discharge sheet becomes unmanageable by being influenced by air blowing, when the discharge sheet moves until bumping into the abutment member, and it is difficult to stack the sheet stably.
In particular, in a sheet, referred to as a long sheet, of which a length in the sheet discharging direction is approximately 700 mm, there is also a concern that the sheet may fall from the stacking tray, since the sheet is easily influenced by air blowing when being discharged, and a landing spot is located on the downstream side, considerably, in the sheet discharging direction.
As a configuration of preventing a landing spot of a discharge sheet from being located on the downstream side in the sheet discharging direction due to air blowing, an apparatus which stops air blowing in the middle of discharging a sheet is described in JP-A-2011-57313. This apparatus blows air to a lower face of a discharge sheet in order to prevent a stacked sheet from being pushed out due to a leading end of the discharge sheet, and stops air blowing immediately before a trailing end of the discharge sheet passes through a discharging roller so that the apparatus prevents a landing spot of the discharge sheet from locating on the downstream side of a stacking tray in the sheet discharging direction.
Here, in general, at a time of discharging a discharge sheet, the stacked sheet is pushed out to the downstream side in the sheet discharging direction due to friction between a lower face of a discharge sheet and a top face of a stacked sheet. Since responsivity of a blower fan which performs air blowing is not so good, in a case of stopping air blowing, an air volume gradually decreases, and air blowing is stopped, finally.
That is, in the apparatus described in JP-A-2011-57313, by gradually decreasing an air volume in the middle of discharging of the discharge sheet in order to stop air blowing, it becomes an air volume in which a lower face of a discharge sheet and a top face of a stacked sheet are subjected to friction contact before a trailing end of the discharge sheet passes through a discharging roller. For this reason, due to friction between the lower face of the discharge sheet and the top face of the stacked sheet, the stacked sheet is pushed out toward the downstream side in the sheet discharging direction.